1. Field of the Invention
The present invention relates to an antenna, and in particular to a tri-band antenna embedded in a mobile electronic device.
2. Description of the Prior Art
In 1999, the wireless local area network (WLAN) market saw the introduction of the 2.4 GHz IEEE 802.11b standard. Today 802.11b and IEEE 802.11a are among several technologies competing for market leadership and dominance.
The wireless 802.11a standard for WLAN runs in the 5 GHz spectrum, from 5.15-5.825 GHz. 802.11a utilizes the 300 MHz of bandwidth in the 5 GHz Unlicensed National Information Infrastructure (U-NII) band. Although the lower 200 MHz is physically contiguous, the Federal Communications Commission (FCC) has divided the total 300 MHz into three distinct 100 MHz realms; low (5.15-5.25 GHz), middle (5.25-5.35 GHz) and high (5.725-5.825 GHz), each with a different legal maximum power output in the U.S.
802.11a/b dual-mode WLAN products are becoming more prevalent up in the market, so there is a growing need for dual-band antennas for use in such products to adapt them for dual-mode operation. A dual-band antenna is a good miniaturized built-in antenna for mobile electronic products. However, the bandwidth of the conventional dual-band antenna is not wide enough to cover the total bandwidth of 802.11a and 802.11b. Generally, because of this narrowband characteristic, the bandwidth of the dual-band antenna can only cover the band of 802.11b and one or two bands of 802.11a.
One solution to the above problem is to provide an antenna for use with low-band, mid-band and high-band signals. For example, U.S. Pat. No. 5,867,131 discloses an antenna comprising three independent dipole pairs for providing respectively three different frequency bands operation. However, each dipole pair is excited in a narrow bandwidth, so this antenna could not cover all frequency bands of 802.11a and 802.11b unless additional dipole pairs are applied, which would increases the complexity of this antenna and the difficulty of matching impedance.
Hence, an improved antenna is desired to overcome the above-mentioned shortcomings of the existing antennas.